@article{fdi:010066005,
  title = {{E}stimation of the driving force for dioxygen formation in photosynthesis},
  author = {{N}ilsson, {H}. and {C}ournac, {L}aurent and {R}appaport, {F}. and {M}essinger, {J}. and {L}avergne, {J}.},
  editor = {},
  language = {{ENG}},
  abstract = {{P}hotosynthetic water oxidation to molecular oxygen is carried out by photosystem {II} ({PSII}) over a reaction cycle involving four photochemical steps that drive the oxygen-evolving complex through five redox states {S}-i (i = 0, ... , 4). {F}or understanding the catalytic strategy of biological water oxidation it is important to elucidate the energetic landscape of {PSII} and in particular that of the final {S}-4 --> {S}-0 transition. {I}n this short-lived chemical step the four oxidizing equivalents accumulated in the preceding photochemical events are used up to form molecular oxygen, two protons are released and at least one substrate water molecule binds to the {M}n4{C}a{O}5 cluster. {I}n this study we probed the probability to form {S}-4 from {S}-0 and {O}-2 by incubating {YD}-less {PSII} in the {S}-0 state for 2-3 days in the presence of {O}-18(2) and ({H}2{O})-{O}-16. {T}he absence of any measurable {O}-16,18(2) formation by water-exchange in the {S}-4 state suggests that the {S}-4 state is hardly ever populated. {O}n the basis of a detailed analysis we determined that the equilibrium constant {K} of the {S}-4 --> {S}-0 transition is larger than 1.0 x 10(7) so that this step is highly exergonic. {W}e argue that this finding is consistent with current knowledge of the energetics of the {S}-0 to {S}-4 reactions, and that the high exergonicity is required for the kinetic efficiency of {PSII}.},
  keywords = {{P}hotosystem {II} ; {W}ater-oxidizing complex ({WOC}) ; {O}xygen-evolving complex ({OEC}) ; {E}quilibrium constant for {S}-4 -> {S}-0 transition},
  booktitle = {},
  journal = {{B}iochimica et {B}iophysica {A}cta-{B}ioenergetics},
  volume = {1857},
  numero = {1},
  pages = {23--33},
  ISSN = {0005-2728},
  year = {2016},
  DOI = {10.1016/j.bbabio.2015.09.011},
  URL = {https://www.documentation.ird.fr/hor/fdi:010066005},
}